Susceptibility of endemic and exotic North American ladybirds (Coleoptera: Coccinellidae) to endemic fungal entomopathogens

Ted E Cottrell,David I Shapiro-Ilan

doi:10.14411/eje.2008.058

Abstract

We tested the laboratory susceptibility of four endemic and two exotic species of North American Coccinellidae to a single rate (2.5 × 10 5 conidia/ml) of Beauveria bassiana derived from different sources. The endemic species Olla v-nigrum, Cycloneda munda and Hippodamia convergens were susceptible to B. bassiana Isolate B which was originally isolated from O. v-nigrum and the rate assayed was known to represent the LC50 against O. v-nigrum. However, neither the endemic C. maculata nor the exotic species Harmonia axyridis and Coccinella septempunctata were susceptible to this isolate at this rate. Additionally, all species of endemic and exotic Coccinellidae used in these assays were resistant to B. bassiana strain GHA and BbAR1 at that rate. We discuss the implications of these results in regard to the establishment of exotic species in new habi tats.

Highlights

A dearth of information exists regarding the relative susceptibility of different species of predaceous Coccinellidae to entomopathogens under natural conditions
Species used in these studies included four coccinellids endemic to North America (O. v-nigrum, C. maculata, Cycloneda munda (Say) and Hippodamia convergens GuérinMéneville) and two coccinellid species that have been introduced into North America (H. axyridis and C. septempunctata) (Gordon, 1985)
No dead C. maculata or H. axyridis ever developed signs of visible mycosis. Regarding those coccinellid species used in these experiments, the endemic O. v-nigrum, C. munda and H. convergens and the exotic C. septempunctata are primarily aphidophagous, whereas the endemic C. maculata and exotic H. axyridis are highly polyphagous (Gordon, 1985; Hodek & HonČk, 1996)

Summary

Introduction

A dearth of information exists regarding the relative susceptibility of different species of predaceous Coccinellidae to entomopathogens under natural conditions. Shapiro-Ilan & Cottrell (2004) showed that the entomopathogenic nematode Steinernema carpocapsae (Weiser) caused significantly less mortality in the exotic H. axyridis than in the endemic species Coleomegilla maculata (Degeer) or O. v-nigrum one day after treatment and significantly less mortality compared with those same two species and the exotic Coccinella septempunctata L. two days after treatment. These examples show that differential susceptibility to entomopathogens exists between coccinellid species that occupy the same habitat and provides insight regarding a species’ potential to become established in new territories. In addition to resistance to endemic entomopathogens by invading species contributing to their successful establishment, higher susceptibility of endemic competitors to endemic entomopathogens could further contribute to the establishment of introduced species

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Conclusion